My rad looked a bit low so I stuck in about half a litre of anti-freeze. I then ran the car in the driveway for twenty minutes or so and when it had cooled down (after reaching a stable temp and with heat coming out of the matrix) I checked and it needed another half a litre.

 

I'm thinking air lock somewhere in the system. I've parked so that the rad is at the highest point of the system - are there any bleed valves or tricks I can use to ensure that I've got all the air out?

 

Cheers.

Yes Barry,

 

Try leaving the bleed valve, RH side of radiator undone and the rad cap off, run the engine and top it up as it needs it while it is running.

 

Try depressing the rad hose with your hand, as there can be air trapped in there causing your system to take ages to fill.

 

Top up the reservoir tank as well!

I find that you usually need to do this a couple of times to get all the air out. I then check the level every day for about a week. (Paranoia etc!)

Cheers for the advice - something to do tomorrow I guess. As if I need an excuse to give her a run!

and leave the heating inside the car on max.

 

Vijay

Top up the reservoir tank as well!

 

Why would you do that? The reservoir tank recieves water from the radiator but doesnt return water to the system. So why fill it up?

Why would you do that? The reservoir tank recieves water from the radiator but doesnt return water to the system. So why fill it up?

 

 

Opinion can be divided on this. Some say that the radiator cap can act as a 2-way valve - it looks a lot like a 1-way one to me, but I haven't tested and/or proven it one way or the other.

Yes it does return it to the water system, the rad cap is a two way valve!

In that the rad cap allows water to flow two ways yes, but how can it draw water from the overflow , as there is a big drain hole in the tank, which would preclude the vaccum required?

No vaccum is required in the overflow tank, the vacuum is achieved by the cooling system, cooling down!

yes, but about three inches down the neck of the over flow tank is a 2inch hole, so the rad would only besucking in any water in the hose and then air

Well I always thought the expansion tank was only used for dumping water and not sucking it back into the cooling system :confused:

when the water expands it is sent to the expansion tank, as the system cools it is syphoned back into the radiator as the air space increases in the rad so a slight vac is made, so causing the syphon

 

 

Pete

Jock the pipe feeds into the base of the overflow tank and not the neck!

OK - the overflow bottle was dryer than a dry thing that's been dried in a desert. So I dumped a litre and half of water and anti-freeze into it. AND then I thought - how much should be in there? The dipstick thingy is not clear - on my next run will I have steam coming out of this? Any thoughts?

The overflow tank is self-regulating...

 

The rest of the coolant system feeds coolant into the BOTTOM of it. Coolant can only get into that overflow tank when the pressure in the system is enough to press the valve on the rad cap upwards enough. If you look in your filler spout you'll see the little hole at the top of it which feeds the overflow tank. You can see that normally the piston-type thing on the rad cap will block it.

 

When the temp/pressure of the coolant drops, that creates a partial vacuum which then starts hoovering up the coolant from the overflow tank again. God knows how that gets past the rad cap... maybe that also moves under negative pressure? Or maybe there's a seperate return path with a check valve in it? (Never noticed a pipe I must say)

 

The height gap between where the rad cap lets water into the overflow bottle and the overflow on the overflow lets it out just gives you a head of fluid to make sure you've got a closed circuit all the time and no air can get in even during suck-back. If it's overfilled, then the top overflow pipe will dribble out under the car and it'll look like you've got a chronic leak, but you haven't. The pipe at the top of the overflow tank really is an overflow - so if you overfill coolant, the water dribbles out of the 'ole instead of launching your rad cap into orbit!

 

If it was totally dry I suspect every time you filled it, took it for a run, and cooled it, the cooling was sucking air back into the system :eek:

 

Incidentally, following the other discussion we just had on WaterWetter, be aware that putting neat antifreeze in as a top-up will lower the cooling capacity of the engine... I'd stick to 50/50 unless you're -sure- the coolant in there is too "watery," or you're expecting a cold snap below -37!

hmm, it seems obvious to me that its a 2 way valve. What would be the point in having the tank at all if it was onyl for dumping water, why not just dump it straight onto the floor?

And why would you check the water level from here, with markings for H & L?

And why would you check the water level from here, with markings for H & L?

 

If it's on "H" it tells you not to worry about any puddles you find under it following a good hard run I suppose, and if it's over "L" it tells you you'll keep the vacuum, and don't worry about that either?

No you won't have steam coming out of there, it will just spill onto the floor, there is a dipstick with your O.F. bottle.

My point exactly - there is a dipstick; it must be there for a reason!!!

http://auto.howstuffworks.com/cooling-system7.htm